exam 2

• Charges


  Positive (+) or negative (-)
• Like charges


  Repel
• Unlike charges


  Attract
• Force between charges


  Stronger when charges are closer
• Electric field


  Explains how charges exert forces at a distance
• Electric field


  1. Charge produces electric field

  2. Another charge experiences the electric force exerted by the field
• Moving charges


  Exert magnetic force on each other
• Current


  Flow of charges
• Currents in the same direction

  Attract
• Opposite currents


  Repel
• Force between currents


  Stronger when charges are closer or when current is stronger
• Magnetic force in magnets

  Comes from electrons spinning and orbiting in the atoms
• Faraday Experiment


  1. Magnet moves through coil

  2. Current is induced in coil

  3. Current stops when magnet stops moving

  4. Current appears in opposite direction when magnet starts moving back

  5. Current stops again when magnet stops moving
• Changing magnetic field induces an electric field
• Maxwell's Equations


  • Electric charges produce electric fields
  • Currents produce magnetic fields
  • Changing magnetic fields produce electric fields
  • Changing electric fields produce magnetic fields
• Maxwell predicted EM waves and calculated their speed as 3.00 x 10^8 m/s
• Hertz experimentally confirmed the speed of EM waves is the same as the speed of light
• The wavelength of an EM wave can be anything
• Ether


  Introduced as the medium of light waves
• Properties of Ether


  • Everywhere
  • Tenuous fluid
  • Extremely stiff
• Michelson-Morley Experiment


  1. Light goes down two paths, then recombine on a screen

  2. Interference pattern is observed

  3. Interference pattern shifts when apparatus is rotated
• The Michelson-Morley experiment was a failure, the expected shift was not observed
• Principle of Relativity


  Laws of physics are the same in all uniformly moving reference frames
• Postulates of Special Relativity

  • Laws of physics are the same in all uniformly moving reference frames
  • Speed of light c = 3.00 x 10^8 m/s is the same in all uniformly moving reference frames
• Event


  Something that occurs at a specific position and time
• Simultaneous events


  Events happening at the same time
• Simultaneity is relative, two events that are simultaneous in one IRF are not simultaneous in another
• Time Dilation


  The proper time is measured in the frame where the two events happen at the same position
• Reference frames


  Inertial reference frames (IRFs) where the laws of physics are the same
• Postulate 2


  The speed of light is the same in all uniformly moving reference frames
• c = 3.00 × 10^8 m/s
• Event


  Something that occurs at a specific position and a specific time
• Events


  • Births, deaths, coughs, crashes, etc.
• Example of simultaneous events


  • Alarm goes off when a light beam is broken
• Simultaneity is relative!
• Two events that are simultaneous in one IRF are not, in general, simultaneous in another
• Events that occur at the same position can be simultaneous in all frames
• Proper time


  The shortest time between two events, measured in the frame where the two events happen at the same position
• Lorentz boost factor (Γ)


  1 / sqrt(1 - (v/c)^2)
• As v approaches c, Γ becomes infinite